Tubing is utilized for fuel lines and vapor return lines in automobiles. It is known to make tubing from multiple layers of synthetic material that can carry fuel and vapor. Each layer of material performs a different function. For example, an innermost layer might be resistant to fuel but allows vapor to pass through the layer. Another layer of different material may not be resistant to direct contact with fuel but provides an excellent vapor barrier. The layers are combined to form a tube that has excellent qualities which are not readily achievable using a single material.
Since vehicles have numerous parts confined in a relatively small volume, tubing must be able to accommodate any protruding parts that prevent the tubing from continuing in a straight line. As vehicles become more crowded with parts, the tubing necessarily must follow a more tortuous path. Thus, it is known to make multi-layer tubing which contains corrugations that are designed to expand and contract thereby allowing the tubing to flex. Flexing provides easier assembly of tubing into the vehicle.
Although corrugations in the tubes provide easier bending and manipulation during assembly, corrugations hinder fluid flow through the tube by creating turbulence. For instance, corrugations in a bend region of a fuel tank inlet hose introduce enough turbulence in the fuel flow that fuel tank filling time is noticeably increased, thereby reducing customer satisfaction.